1. Field of the Invention
The present invention relates to an information recording medium, such as an optical disc, and an apparatus for and a method of reproducing information from the information recording medium.
2. Description of the Related Art
In an optical disc represented by a Compact Disc (CD) and a DVD, the long or short length of a pit is used to record information. However, in order to record information for copy control for the prevention of illegal copying or the like, there is a request for reserving another recording area without decreasing a recording capacity by the pit.
As a method of increasing the recording capacity by other means except the method using the long or short length of the pit, there is known a technique of displacing or shifting the position of the pit in the radial direction of the optical disc. This technique is such that information is recorded by wobbling the position of the pit in the radial direction of the optical disc and by performing spread spectrum with respect to the wobble (e.g. Japanese Patent Application Laying Open NO. 2003-85896).
This technique is such as to append a synchronization signal to predetermined data including the information for copy control, perform spread spectrum with respect to this data by using random data to thereby generate a wobble signal, and wobble the position of a record mark according to the wobble signal. In this case, since the wobble is spread in spectrum, it is possible to increase the concealment of the predetermined data to some extent.
The synchronization signal has a particular data pattern and is appended to the predetermined data with a constant cycle. Therefore, although the predetermined data is spread in spectrum and randomized, there is the possibility that the wobble signal is reproduced from the optical disc and that the synchronization signal with the particular data pattern is detected from the reproduced wobble signal. This causes the problem that a predetermined data block is extracted on the basis of the synchronization signal, which gives a clue to the analysis of the information for copy control associated with information about copyright or the like.